Gas-blast downstream-type of high-voltage circuit breaker having field-controlling shields and single venting movable contact

ABSTRACT

In a circuit breaker of the live tank type SF6, or other gas, is contained in the tank of high-pressure. Two hollow seriesconnected movable contacts bridge stationary contacts inside the tank. A double break is provided and two stationary shields are provided per break-to give a substantially uniform voltage gradient across the contacts in the open position. Capacitors are used to divide the voltage across the open contacts. A probe arrangement is used to insert resistors into the circuit to reduce the rate of rise of recovery voltage. The shields are contoured to establish a high velocity flow of gas into the arc region. Flow of gas from the high pressure tank through the hollow contacts into a low pressure chamber is controlled by a down stream blast value. Double flow of the gas can be obtained by providing secondary downstream valves and hollow contacts in each bushing in addition to the main downstream valve.

United States Patent 1 Fischer et a1.

[54] GAS-BLAST DOWNSTREAM-TYPE OF HIGH-VOLTAGE CIRCUIT BREAKER HAVINGFIELD-CONTROLLING SHIELDS AND SINGLE VENTING MOVABLE CONTACT [75]Inventors: William H. Fischer, Pittsburgh; Charles F. Cromer, Trafford,both of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Oct. 28, 1968 [21] Appl. No.: 771,113

[52] U.S. Cl. ..200/l48 B, 200/148 H [51] Int. Cl. ..H01h 33/54 [58]Field of Search ..200/148,148.8,l48.2,148.4

[56] References Cited UNITED STATES PATENTS 3,164,705 l/l965 Cromer..200/148 B 3,286,066 11/1966 Floessel .....200/l48 B 3,454,734 7/1969Colclaser, Jr. et al ..200/l48.8

FOREIGN PATENTS OR APPLICATIONS 748,225 4/1956 Great Britain ..200/l4851 Apr. 3, 1973 Primary ExaminerRobert S. Macon Att0rneyA. T. Stratton,C. L. McHale and W. R. Crout [57] ABSTRACT In a circuit breaker of thelive tank type SP or other gas, is contained in the tank ofhigh-pressure. Two hollow series-connected movable contacts bridgestationary contacts inside the tank. A double break is provided and twostationary shields are provided per break-to give a substantiallyuniform voltage gradient across the contacts in the openposition.Capacitors are used to divide the voltage across the open contacts. Aprobe arrangement is used to insert resistors into the circuit to reducethe rate of rise of recovery voltage. The shields are contoured toestablish a high velocity flow of gas into the are region. Flow of gasfrom the high pressure tank through the hollow contacts into a lowpressure chamber is controlled by a down stream blast value. Double flowof the gas can be obtained by providing secondary downstream valves andhollow contacts in each bushing in addition to the main downstreamvalve.

16 Claims, 15 Drawing Figures HIGH PRESSURE SP6 GAS' 19.

LOW PRESSURE sF GAS PATENTEDAPRQ 197a SHEET 1 [IF FIG.|.

Es RA w s s S ES E R R Dr D.-

w w L m HIGH PRESSURE INVENTORS Charles F. Cromer and William H. FischerBY 2 ATTORNEY m N s G E 6 E 4 P 0 2 S 2 2 a a E. W ES & mm W 6 my a J HP w M w w f U PATENTEUAPM 191a 3,725,623

SHEET 3 or 6 HIGH PRESSURE SF6 GAS vH LOW PRESSURE sF GAS LI 2 L2 HIGHPRESSURE SF5 GAS 51 45 n 4s 57 54 54 g x 52 53 24 25 27 n LOW PRESSURESF GAS v PATENTEDAPR3 197a SHEET l 0F 6 FIG.9.

LOW PRESSURE SP GAS FIG.H.

FLEXIBLE/ PATENTEDAPRB 197s 3,7 5,523

sum 5 BF 6 FIG.|2.

HIGH PRESSURE SF GAS FIG. l4.

PATENTEUAPR3 I975 SHEET 6 BF 6 m: 5/ \AA////////////// A E I mmDmwwmmIQ:

GAS-BLAST DOWNSTREAM-TYPE OF HIGH- VOLTAGE CIRCUIT BREAKER HAVING FIELD-CONTROLLING SHIELDS AND SINGLE VENTING MOVABLE CONTACT BACKGROUND OF THEINVENTION This invention relates, generally, to circuit breakers and,more particularly, to circuit breakers of the compressed-gas typesuitable for extra-high-voltage (EHV) service.

, Prior EHV circuit breakers have required a plurality of modules orinterrupting units per phase. For example, a recent breaker for SOOKVservice has three series-connected modules per phase. An object of thisinvention is to provide a single module 345KV, 50,000 amperesinterrupting capacity compressed-gas breaker unit, thereby reducing thecost of EHV circuit breakers.

Another object of the invention is to provide a double-breakcompressed-gas circuit interrupter having a downstream valve forcontrolling the flow of interrupting gas through the contacts of theinterrupter.

A further object of the invention is to provide a double-break,downstream double-flow compressed-gas circuit interrupter.

Still another object of the invention is to provide means for operatingthe downstream valves of the in terrupter.

A still further object of the invention is to provide for insertingresistance means in parallel with the interrupting arcs to reduce therate of rise of recovery voltage.

Another object of the invention is to provide static shields in theinterrupter which give a substantially uniform voltage gradient acrossthe contacts in the open position.

A further object of the invention is to utilize the shields to establisha high velocity flow of gas into the contact.

Other objects of the invention will be explained fully hereinafter orwill be apparent to those skilled in the art.

SUMMARY OF THE INVENTION In accordance with one embodiment of theinvention, sulfur-hexafluoride (SP6) gas is contained in a tank at arelatively high pressure. Relatively stationary contacts are mounted onthe inner ends of two bushings extending through opposite ends of thetank. Two hollow series-connected movable contacts bridge the stationarycontacts when in the closed position. A double break is provided whenthe movable contacts are separated from the stationary contacts. Twostationary metal shields are provided per break to give a substantiallyuniform voltage gradient across the contacts in the open position. Acylindrical portion of each movable contact passes through two shields.A resistor probe in one of each pair of shields inserts a resistor inparallel with the interrupting arc, thereby reducing the rate of rise ofrecovery voltage. The shields are contoured tacts into a low-pressurechamber is controlled by a downstream blast valve. Double flow of thegas can be obtained by providing secondary downstream valves and hollowcontacts in each busing in addition to the main downstream valve.Various methods for operating the secondary valves are disclosed.Capacitors are provided to divide the voltage across the open contacts.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of thenature and objects of the invention, reference may be had to thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic view of an interrupter head and supportingstructure embodying principal features of the invention;

FIG. 2 is a diagrammatic view of an interrupter head in which themovable contacts are carried by a rotatable bridging cross-arm;

FIG. 3 is a detail view showing the contact and shield arrangementutilized in FIG. 2;

FIG. 4 is an end view of one of the movable contacts for the structureshown in FIG. 2;

FIG. 5 is a view, partly in elevation and partly in section of thecontact shown in FIG. 4;

FIG. 6 is 'a view, similar to FIG. '3, showing a modified shieldarrangement;

FIG. 7 is a view, similar to FIG. 2, showing the location of downstreamvalves for double flow of the interrupting gas;

FIG. 8 is a diagrammatic view of an interrupter head havingreciprocating contacts;

FIG. 9 is a detail view showing the contact and shield arrangementutilized in FIG. 8;

FIG. 10 is a detail view showing an electromagnetic method of operatinga secondary downstream valve;

FIGS. 11 and 12 are detail views showing alternate electromagneticmethods of operating the valves;

FIG. 13 is a detail view showing a mechanical method of operating adownstream valve;

FIG. 14 is a diagrammatic view showing a downstream valve operated byfluid-pressure; and

FIG. 15 is a view, in section, of a prototype interrupter embodyingfeatures of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, andparticularly to FIG. I, the circuit breaker 10 shown therein may begenerally of the type described in US. Pat. No. 3,291,947 issued Dec.13, 1966 to R. C. Van Sickle and assigned to' the Westinghouse ElectricCorporation. As shown in FIG. I, the circuit breaker 10 comprises ametal tank or interrupting head 11 having a terminal bushing12'extending through each end of the tank 12, an intermediate chamber 13located at the bottom of the tank 11 and connected to the tank through amain'blast valve, shown diagrammatically at 14, and a hollow insulatingcolumn 15 having a cap attached to the chamber 13 for supporting thetank 11 and the chamber l3-and insulating them from ground. The tank 11contains a high-dielectric-strength interrupting gas,

sure reservoir, which is not shown, is connected to the tank 11 by aninsulating high-pressure feed pipe 18. An

operating rod 19 connects a main operating mechanism (not shown) with amechanism for operating the contacts of the interrupter located insidethe tank 11. As shown, the feed pipe 18 and the operating rod 19 arelocated inside the vertical insulating column 15.

As shown in FIG. 2, a stationary contact member 21 is mounted on theinner end of each terminal bushing 12. A hollow cross arm 22 isrotatably mounted on a hollow bearing support 23 mounted inside the tank11. Theblast valve 14 may be located inside the bearing support 23 andoperated when the arm 22 is rotated in the .manner described in theaforesaid Van Sickle patent. Each end of the arm 22 has a generallycylindrical portion 24 thereon which engages one of the stationarycontacts 21 when in the closed position. In the closed position currentis carried by one of the terminal bushings 12 through a stationarycontact 21, a movable contact 24, the arm 22, the other movable contact24, and the other stationary contact 21 to the other terminal bushing12. Line conductors 21, 22 may be con nected to the outer terminals ofthe bushings 12. When the arm 22 is rotated in a direction to open thecontacts, the circuit is interrupted at two places, thereby providing adouble-break of the circuit.

In order to give a more uniform voltage gradient across the contacts inthe open position, two stationary:

contoured shields are provided per break. One shield 25 is spaced fromeach stationary contact 2l and is supported by an insulator 27 attachedto the inside wall of the tank 11. The other shield 26 of each pair ofshields is spaced from the shield 25 and is supported by a bracket 28attached to the inside wall of the tank 11. One cylindrical contactportion 24 of the rotatable arm 22 passes through the two shields 25 and26 of each pair of shields when in the closed position.

In order to reduce the rate of rise of recovery voltage, a resistor 29is connected in parallel with the interrupting arc during interruptionof the main arc. As' shown more clearly in FIG. 3, a spring-biasedcontact member 31 is slidably disposed in the shield 25 to engage themoving contact member 24 when it passes through the shield 25. Thecontact member 31 is connected to one terminal of the resistor 29, andthe other terminal of the resistor 29 is connected to the stationarycontact 21 as shown in FIG. 2. When the breaker opens to interrupt afault, an arc is drawn between the moving contact 24 and the stationaryfollower contact 36. The contact or resistor probe 31 is in contact withthe moving contact 24 while it is being drawn through the shield 25,thereby connecting the resistor 29 in parallel with the interruptingarc. The interrupting arc is extinguished by the time, the movingcontact leaves the shield 25.

Duringthe interrupting operation, the downstream valve 141is opened topermit the high pressure gas to flow from inside the tank 1 1 throughthe hollow arm 22 and the valve 14 into the intermediate chamber l3.- Asshown in FIG. 3, the end portion 32 of the stationary contact 21 isgenerally convex in shape. A surface of the shield 25, which is spacedfrom, and faces the convex surface 32, is generally concave in shape, asshown at 33. Thus, the contact 21 and the shield 25 are so spaced andcontoured as to establish a high-velocity flow of gas into the arcregion and to direct the gas into the hollow moving contact portion 24,thereby insuring that the arc terminals will remain on the moving andstationary contacts.

As shown in the modified construction of FIG. 6, the shield 26' may beprovided with a concave surface 34, which faces and is spaced from aconvex surface ,35 on the shield 25. Thus, a high-velocity flow of gasis also established into the resistance arc region should this becomenecessary to stabilize the arc position.

Referring again to FIG. 3, a spring-biased contact follower 36 isslidably disposed in the end of arrows stationary contact member 21. Thefollower 36 is engaged by contact fingers 37 disposed in the contactmember 21.,The structure of the follower 36 and the fingers 37 is shownin more detail in FIG. 15. The follower 36 is biased outwardly by aspring 38, the outward movemerit being limited by a flange 39 on theinner end of the follower 36. The outer end of the follower 36 has aprojection 41 thereon, thereby providing an inwardly curved surface 42on the outer end of the follower 36. As shown more clearly in FIGs. 4and 5, the hollow cylindrical end of the movable contact 24 is dividedinto a plurality of segments 43, each one of which has a portionextending radially inwardly with a curved surface 44 thereon, whichcooperates with the curved surface 42 on the follower 36 to provide aninwardly bending loop 48 in the path of the arc current flowing throughthe contact members when they are separated. As' shown by the arrow inFIG. 5, a magnetic force on the arc has a tendency to drive the are intoor toward the center of the moving contact, thereby aiding in the In theinterrupter shown in FIG. 7, which is similar to the interrupter shownin FIG. 2, a secondary downstream valve 51 is provided at eachstationary contact 21, thereby improving the performance of theinterrupter 11 by double flow of the interrupting gas through thecontacts 21, 24, as indicated by the arrows in FIG. 9. The structure andthe manner of operation of the secondary valve 51 will be described morefully hereinafter.

In the modified interrupter shown in FIG. 8, the movable contact members24 are of the reciprocating type. They are slidably disposed in acentral housing 52 and are operated by a linkage mechanism 53, which, in

turn, is actuated by the operating rod 19. The main blast valve 14 canbe actuated by the operating mechanism in the manner described in theaforesaid copending application. Contact fingers 54 are provided in thehousing 52 for slidably engaging the moving contact members 24'. Asecondary downstream blast valve 51 is provided in each terminal bushing12.

As shown more clearly in FIG. 9, a hollow double flow contact 55 isprovided in each stationary contact member 21. A passageway 56 extendingthrough the contact member 21 permits gas to fiow to the downstreamvalve 51 shown in FIG. 10. A downstream filter and baffle 57 enclosesthe secondary downstream valve 51. The shield 25 is similar to the onepreviously described. The shield 26" is incorporated in the 'centralhousing 52 as shown in FIG. 8. These shields function in the mannerpreviously described to give a more uniform voltage gradient across thecontacts in the open position. The hollow contacts 24' and the centralhousing 52 bridge the two bushings and are at tank potential. The hollowcontacts extend through the shields in the breaker closed position.

In the breaker closed position the current is carried from onestationary contact through the hollow contacts and central housing tothe other stationary contact. When the breaker opens to interrupt afault, an arc is drawn between the moving contact and the stationarycontact. At the same time, or slightly before, the downstream valves areopened and SF flow is established into the hollow contacts. Aspreviously explained, double-flow interrupters have been proven to givegood performance. The baffle and filter 57 which is located downstreamof the stationary contact reduces bushing contamination and alsoprevents a direct blast on the bushing.

There are three general ways in which the stationary contact downstreamvalve 51 can be operated. They are: (l) Electromagnetic (2) Mechanical(3) Fluid or Gas. An electromagnetic means is shown in FIG. 10. Thevalve 51 is generally cylindrical in shape and is slidably mounted on anenlarged portion 61 of the conductor 55. The valve is biased to theclosed position by a spring 62. When the valve is opened, gas ispermitted to flow through openings 63 in the conductor 55 into thefilter 57 which surrounds the valve. An induction ring or coil 64 isattached to the one end of the valve 51. Another induction ring or coil65 is mounted on an enlarged portionvof the conductor 55 and isinsulated from the conductor by insulation 66. The valve is opened whena sufficiently high magnitude of fault current flows through theconductor 55, thereby inducing current in the rings or coils 64 and 65.This current produces a flux which creates an attractive force betweenthe rings or coils, thereby opening the valve against the force of thespring 62. The distance between the coils should be relatively small tomake them fast and effective.

Another method of operating the downstream secondary valve is showndiagrammatically in FIG. 11. The main conductor 55 carries the currentto be interrupted. A flexible conductor 67 physically and electricallyparallels the conductor 55. A link 68 mechanically connects theconductor 67 to a pivotally mounted lever 69 which, in turn, isconnected to thevalve (not shown) by means of a link 71. When asufficiently high magnitude of fault current flows through theconductors they attract each other, thereby actuating the linkagemechanism to operate the valve.

Still another method for operating the secondary valve 51 is shown inFIG. 12. The end portion 55 is insulated from the remainder of theconductor 55 by insulation 72. The driving coils 64 and are connectedbetween the insulated portion 55 and the main I conductor 55. When themoving contact member 24' separates from the contact fingers 37 the arc73 transfers to the contact portion 55' which functions as an arc probe,thereby energizing the driving coils 64 and 65' to operate the valve inthe manner hereinbefore described.

A mechanical method of operating the valve 51 is shown in FIG. 13. Anactuator 74 moves with the moving contact member 24'. The valve 51 isslidably disposed on an enlarged portion 75 of the stationary conductor55. The valve is biased to the open position by the spring 62' disposedin a recess in the baffle 57' which encloses the valve structure. A sealfollower 76 is slidably disposed on the enlarged portion 61 of theconductor 55. The follower 76 is biased to the right towards the valve51 by a spring 77 disposed between a shoulder 78 on the conductor 55 andthe left hand end of the cylindrical seal 76. The travel of the seal islimited by a cross member 79 inside the seal and extending throughoppositely disposed slots 81 in the conductor 55. A dashpot 82 isconnected to the cross member 79. The dashpot is so constructed that itprovides a delayed movement of the seal 76 to the right and permits afree return movement to the left. Delayed movement of the seal 76 couldalso be accomplished by increasing its weight to increase its inertia.The valve 51 is shown in full lines in the breaker open position. Whenthe breaker is closed, the actuator 74 moves to the left, thereby movingthe valve 51 to the left, as shown by the dash lines, to engage the seal76, thereby preventing gas flow through the openings 63 in the conductor55. When the breaker is opened, the actuator 74 moves to the rightpermitting the spring 62 to open the valve 51 and permit gas flowthrough the openings 63. After a predetermined time interval the sealfollower 76 is moved to the right by the spring 77 to engage the end ofthe valve 51 and stop the flow of gas through the openings 63. Thedelayed action of the seal is obtained by the dashpot 82 in the mannerhereinbefore described. When the breaker closes the dashpot permits theseal to move freely to the left along with the valve 51. Thus, the sealfollower stops the flow of gas after the interrupting operation iscompleted.

Another method of actuating the valve 51 is by a fluid-pressure actuatedpiston controlled either directly or by a pilot valve. A pilot scheme isshown diagrammatically in FIG. 14. The valve 51 is connected to a piston85 disposed in a cylinder 86. A spring 87 biases the piston 85 and thevalve 51 to its closed position. One end of the cylinder 86 is connectedby a line 88 to an enclosure 89 having a pilot valve 91 inside theenclosure. The valve 91 is biased to the closed position by a spring 92and it may be opened either by induction coils 93 and 94 as shown, or bya mechanical actuator. The induction coils are energized by the currentflowing through the main conductor 55. High pressure fluid, such as thehigh pressure interrupting gas, is applied to an opening 95 in theenclosure 89.

When the breaker opens under fault conditions, the high current in theconductor 55 energizes the induction coils 93 and 94, which are wound torepel" each other, thereby opening the pilot valve 91 and admitting highpressure gas to the cylinder 86 to open the valve 51 which permits thehigh pressure gas from the contact region to flow past the valve 51 intothe low pressure region inside the baffle 57. When the arc is interrupted and current ceases to flow in the conductor 55, the inductioncoils 93 and 94 are deenergized and the spring 92 recloses the pilotvalve 91, thereby stopping the flow of high pressure gas to the cylinder86. The cylinder 86 exhausts through a bleed hole or restricted portion96 in an extension 97 of the line 88 which is connected to the lowpressure region. After a time delay, the valve 51 is reclosed by thespring 87, thereby stopping the flowof gas past the valve.

A prototype interrupter 100 embodying features of the present inventionis shown in H0. 15. The interrupter 100 is of the double flow downstreamtype. This interrupter has been tested in a laboratory of the assigneeof this application. The interrupter comprises a metal cylinder 101, astationary contact 21', a'movable contact 24', a static shield 25' and adownstream blast valve 14'. The stationary contact 21' is supported onone end of an insulating sleeve 102 the other end of which terminates ata metal cover 103 having an opening 104 therein through which hollowconductor 55 extends. The contact 21 is connected to the inner end ofthe conductor 55 which may extend through a terminal bushing (notshown). An insulating sleeve 105 surrounds the conductor 55' outside ofthe cover 103. The cover 103 is attached to a ring 106 by bolts 107. Thering 106 may be welded in the end of the cylinder 101. A cover 108 isattached to the cover 103 to close an access opening 109 in the cover103. A ring 111 is welded in the other end of the cylinder 101 and acover 112 is attached to the ring 111 by bolts 113. A cover plate 114 isattached to the cover 113 to close an access opening 115 in the cover113. A valve seat 116 is provided in the cover plate 114 for the valve14'. A conducting sleeve 117 is attached to the cover 112 by bolts 118.An end cover 119 is attached to the sleeve 117 by screws 121.Spring-biased contact fingers 54', which slidably engage the movablecontact 24', are retained in position by the end cover 119. A flangedsleeve 122 is attached to the end cover 119 by bolts 123. The staticshield 25 is attached to the flanged end 124 of the sleeve 122 by screws125. The movable contact member 24 may be reciprocated inside thesleeves 122 and 117 by means of a lever 126 which is driven by a shaft127 extending to the outside of the cylinder 101. The lever 126 may beattached to the contact 24' by means of a pin 128 disposed in anelongated slot 129 at one end of the lever 126.

When the contact members of the interrupter are closed, a current paththrough the interrupter extends from the conductor 55' through thestationary contact 21 which includes the contact follower 36 and thecontact fingers 37', then through the movable contact 24 and the contactfingers 54' to the sleeve 117 and then through the cover 112 and thecover plate 114 which may be connected to a power conductor. Thecylinder 101 contains SF gas at a relatively high pressure, for example,200 psi. The region outside the cover plate 1 14 may be enclosed by anenclosure (not shown) for containing the gas at a low pressure. When themovable contact member 24' is separated from the stationary contact 21'and the blast valve 14' and a secondary downstream valve, such as thevalve 51 previously described, are opened, the high pressure gas flowsbetween the surfaces of the stationary contact 21' and the static shield25 into the hollow movable contact 24' and out through the blast valve14' in the manner hereinbefore described. The gas also flows through thehollow stationary contact 21 and conductor 55' as previouslydescribedfThus, a double-flow downstream interrupter is provided whichgave very good performance on tests. As explained hereinbefore, theperformance can be increased or improved by adding a secondarydownstream valve to provide double flow of the interrupting gas in themanner hereinbefore described.

From the foregoing description it is apparent that the inventionprovides a circuit interrupter which is suitable for extra high voltageservice. The cost of a high voltage circuit breaker is reduced byreducing the number of modules or interrupting units required for agiven voltage. The static shields provide a substantially uniformvoltage gradient across the open contacts, thereby enabling theinterrupter to withstand a high voltage per break. The static shieldsalso funtion to establish a high velocity flow of gas into the arcregion, thereby insuring that the arc terminals will remain on themoving and double-flow contacts. There is no bridging insulation acrossthe open contact other than the porcelain bushings and voltage dividerseven though two downstream valves are provided. The electromagneticmethods of valve operation have the advantage of dumping the pressuredownstream of the contacts well in advance of contact separation. Theyuse double flow only when needed, that is, at high fault currents. Aresistor for reducing the rate of rise of recovery voltage isincorporated without the use of auxiliary contact operation. Highdensity gas is maintained at the contacts with substantially no pressuredrop of the gas, thereby improving the interrupting performance. Adownstream valve interrupter has high pressure SP gas available at thecontacts right away. There is no delay as with an upstream type. Theinterrupter is relatively simple in structure with a minimum of partswhich may be readily manufactured and assemoperating requiring notlinkage, etc. It has a still further advantage which is quite important.When the breaker is called on to interrupt a highly inductive orcapacitive low magnitude current, it is very desirable not to chop orforce the current to zero before it normally would. Since in this designonly one valve of the doubleflow design would operate at low currents,the tendency to chop or force an early zero would be greatly reduced.

Since numerous changes may'be made in the abovedescribed constructionand different embodiments of the invention may be made without departingfrom the spirit and scope thereof, it is intended that all subjectmatter contained in the foregoing description or shown lustrative andnot in a limiting sense.

We claim as our invention: 1. In a circuit interrupter, in combination,a metal tank containing an interrupting gas at a relatively highpressure, terminal bushings extending through opposite ends of the tank,a hollow stationary contact supported by the inner end of each bushing,hollow movable contacts for engaging the stationary contacts toestablish a circuit through the interrupter, means for actuating themovable contacts to interrupt the circuit at two breaks, a main blastvalve controlling the flow of gas from inside the tank through themovable contacts to the exterior of the tank, and a secondary blastvalve at each stationary contact responsive to the current flow throughthe interrupter controlling the flow of gas from inside the tank throughthe stationary contacts to the exterior of the tank during interruptionof the circuit.

2. The combination defined in claim 1, including electromagnetic meansfor operating the secondary blast valves.

3. The combination defined in claim 2, wherein the electromagnetic meansis inductively energized by the current to be interrupted.

4. The combination defined in claim 1, including a main conductor forthe current to be interrupted, a flexible conductor physically andelectrically paralleling the main conductor, and linkage means connectedto the flexible conductor for operating a secondary blast valve.

5. The combination defined in claim 1, including an arc probe at eachstationary contact, and electromagnetic means connected to the arc probeto be energized by the arc current to operate'a secondary blast valve.

6. The combination defined in claim 1, including mechanical means foroperating the secondary blast valves, and time delay means for stoppingthe flow of gas a predetermined time after the secondary valves areopened.

7. The combination defined in claim 1, including fluid-pressureactuating means for opening the secondary blast valves, and means forreclosing the secondary valves a predetermined time after interruptionof the circuit.

8. The combination defined in claim 1, including a cross arm rotatablymounted in the tank, and wherein the hollow movable contacts are on theends of the cross arm, and the circuit through the interrupter is in- 10terrupted at two breaks when the cross arm is rotated in one direction.

9. The combination defined in claim 1, including a central housingdisposed within the tank, and wherein the hollow movable contacts arereciprocably disposed in the central housing, and including linkagemeans for actuating said movable contacts.

10. The combination defined in claim 9, wherein the central housingconnects the movable contacts in series-circuit relation.

11. A compressed-gas circuit interrupter including, in combination,stationary contact means, first shield means spaced away from saidstationary contact means and having a first orifice opening providedtherethrough, resistance contact means disposed within said firstorifice opening, resistance means electrically connected between saidstationary contact means and said resistance contact means for loweringthe rate of rise of the recovery-voltage transient during the openingoperation, second shield means havin a second orifice openingtherethrough, a movable tu ular venting contact movable through saidsecond orifice opening and through said first orifice opening and alsointo contacting engagement with the stationary contact means during theclosing operation, whereby during the opening operation a resistance areis established between the movable tubular venting contact and theresistance contact means, means for forcing a blast of compressed gasthrough the movable tubular venting contact to effect extinction of theresistance arc, and the two shield means directing the gas flow duringthe opening operation and additionally providing a substantially uniformvoltage gradient across the separated contacts in the open-circuitposition.

12. The combination according to claim 11, wherein venting means isadditionally provided through the stationary contact means.

13. The combination according to claim 12, wherein a secondaryblast-valve is associated with the venting means through the stationarycontact means.

14. The combination of claim 13, wherein the secondary blast-valve iselectromagnetically operated.

15. The combination of claim 13, wherein a filter surrounds thesecondary blast-valve.

16. The combination of claim 14, wherein induction coils are utilized.

1. In a circuit interrupter, in combination, a metal tank containing aninterrupting gas at a relatively high pressure, terminal bushingsextending through opposite ends of the tank, a hollow stationary contactsupported by the inner end of each bushing, hollow movable contacts forengaging the stationary contacts to establish a circuit through theinterrupter, means for actuating the movable contacts to interrupt thecircuit at two breaks, a main blast valve controlling the flow of gasfrom inside the tank through the movable contacts to the exterior of thetank, and a secondary blast valve at each stationary contact responsiveto the current flow through the interrupter controlling the flow of gasfrom inside the tank through the stationary contacts to the exterior ofthe tank during interruption of the circuit.
 2. The combination definedin claim 1, including electromagnetic means for operating the secondaryblast valves.
 3. The combination defined in claim 2, wherein theelectromagnetic means is inductively energized by the current to beinterrupted.
 4. The combination defined in claim 1, including a mainconductor for the current to be interrupted, a flexible conductorphysically and electrically paralleling the main conductor, and linkagemeans connected to the flexible conductor for operating a secondaryblast valve.
 5. The combination defined in claim 1, including an arcprobe at each stationary contact, and electromagnetic means connected tothe arc probe to be energized by the arc current to operate a secondaryblast valve.
 6. The combination defined in claim 1, including mechanicalmeans for operating the secondary blast valves, and time delay means forstopping the flow of gas a predetermined time after the secondary valvesare opened.
 7. The combination defined in claim 1, includingfluid-pressure actuating means for opening the secondary blast valves,and means for reclosing the secondary valves a predetermined time afterinterruption of the circuit.
 8. The combination defined in claim 1,including a cross arm rotatably mounted in the tank, and wherein thehollow movable contacts are on the ends of the cross arm, and thecircuit through the interrupter is interrupted at two breaks when thecross arm is rotated in one direction.
 9. The combination defined inclaim 1, including a central housing disposed within the tank, andwherein the hollow movable contacts are reciprocably disposed in thecentral housing, and including linkage means for actuating said movablecontacts.
 10. The combination defined in claim 9, wherein the centralhousing connects the movable contacts in series-circuit relation.
 11. Acompressed-gas circuit interrupter including, in combination, stationarycontact means, first shield means spaced away from said stationarycontact means and having a first orifice opening provided therethrough,resistance contact means disposed within said first orifice opening,resistance means electrically connected between said stationary contactmeans and said resistance contact means for lowering the rate of rise ofthe recovery-voltage transient during the opening operation, secondshield means having a second orifice opening therethrough, a movabletubular venting coNtact movable through said second orifice opening andthrough said first orifice opening and also into contacting engagementwith the stationary contact means during the closing operation, wherebyduring the opening operation a resistance arc is established between themovable tubular venting contact and the resistance contact means, meansfor forcing a blast of compressed gas through the movable tubularventing contact to effect extinction of the resistance arc, and the twoshield means directing the gas flow during the opening operation andadditionally providing a substantially uniform voltage gradient acrossthe separated contacts in the open-circuit position.
 12. The combinationaccording to claim 11, wherein venting means is additionally providedthrough the stationary contact means.
 13. The combination according toclaim 12, wherein a secondary blast-valve is associated with the ventingmeans through the stationary contact means.
 14. The combination of claim13, wherein the secondary blast-valve is electromagnetically operated.15. The combination of claim 13, wherein a filter surrounds thesecondary blast-valve.
 16. The combination of claim 14, whereininduction coils are utilized.